The Cathedral or Basilica B (the church was called basilica B before the discovery of the baptistery and the episcopal palace) is built inside the fortification of Viktorinos. It includes the basilica itself, the baptistery and the episcopal palace. The Basilica, in its final state, is in plan and volume more complex than the other churches in Byllis. It consists of three naves, with a semi circular apse, transept, a narthex, an exonarthex, a triportique atrium. This basilica is built at the end of the 4th century, beginning of the 5th century. It has a length of 67 m.

In the junction of the southern and western portals a pear-shaped tank has been found. Like other tanks in Byllis, it was carved into the rock. The depth of the tank is 7,50 m and its circular base has a diameter of 2,45 m. Between the tank and the South Gate portico, a treasure of mints was discovered scattered over an area of 1,50 m2. Aside the coins were collected musical instruments (cymbals, gongs, bells. On the floor of the annexes were collected fragments of pottery dated to the sixth century.

The soils of the nave of the sanctuary of the north wing of the narthex and exonarthex were covered with mosaics, while other floors were paved with stones.

The baptistery occupies the central part of the complex located south of the southern nave. The episcopal palace is located at the South-East of the Cathedral.